576 ALICE JOHNSON AND LILIAN SHELDON. 
of two lateral parts, which are the limbs of the horse-shoe. 
We find that the pituitary body and stomodzeum develope in 
exactly the same way in the Frog as in the Newt. 
The pituitary body has been described as originating from a 
solid ingrowth of epiblast in Teleosteans by Hoffmann (13), 
and it seems to arise somewhat similarly in Lepidosteus (2). 
Gotte also describes the same method of development in Bom- 
binator (9). (See his figs. 127, 128, 250, 252, 292, 293, 298, 
and 305.) 
Tue Tuyroiw Bopy. 
From the hind end of the stomodzeum proceeds a solid cord 
of cells continuous along its dorsal border with the fore-gut 
(figs. 9, 10,11). This is the thyroid body. Later a groove 
is continued into it from the fore-gut, and its hind part 
becomes a tube by the folding over of the edges of the groove. 
Subsequently the hind end is completely constricted off from 
the gut. We have not followed its development further. 
Scott and Osborn (19) described it as being formed from a 
fusion of hypoblast and epiblast in the median ventral line. 
We think that this fusion is the stomodzum, with which the 
thyroid is continuous at its front end, and that the thyroid 
itself is developed in a perfectly normal manner. 
DEVELOPMENT OF PERIPHERAL NERVOUS SYSTEM. 
There is no trace of the peripheral nervous system until the 
neural caval has completely closed and become separate from 
the external epiblast. Fig. 15 represents a transverse section 
through an embryo of a stage just before the closure, showing 
the epiblast in close contact with the neural canal, with which 
its two layers are of necessity continuous at this time. 
The appearance of the peripheral nervous system is preceded 
by the formation of a neural ridge. In an embryo in which 
this is first seen, the neural canal has lost all connection with 
the epiblast in the region of the neural ridge, but remains 
connected with it in the median dorsal line behind the ridge, 
